Milling downhole components generates debris that needs to be removed from circulating fluid. Fluid circulation systems featuring flow in different directions have been tried. One design involves reverse circulation where the clean fluid comes down a surrounding annulus to a mill and goes through rather large ports in the mill to take the developed cuttings into the mill to a cuttings separator such as the VACS tool sold by Baker Oil Tools. Tools like the VACS cannot be used above a mud motor that drives the mill and can only be used below a mud motor when using a rotary shoe. Apart from these limitations the mill design that requires large debris return passages that are centrally located forces the cutting structure to be mainly at the outer periphery and limits the application of such a system to specific applications.
The more common system involves pumping fluid through a mandrel in the cuttings catcher so that it can go down to the mill and return up the surrounding annular space to a discrete passage in the debris catcher. Usually there is an exterior diverter that directs the debris laden flow into the removal tool. These designs typically had valves of various types to keep the debris in the tool if circulation were stopped. These valves were problem areas because captured debris passing through would at times cling to the valve member either holding it open or closed. The designs incorporated a screen to remove fine cuttings but the screen was placed on the exterior of the tool putting it in harms way during handling at the surface or while running it into position downhole. These designs focused on making the mandrel the main structural member in the device which resulted in limiting the cross-sectional area and the volume available to catch and store debris. This feature made these devices more prone to fill before the milling was finished. In the prior designs, despite the existence of a screen in the flow stream through the tool, some fines would get through and collect in the surrounding annulus. The fixed debris barriers could get stuck when the tool was being removed. In some designs the solution was to removably mount the debris barrier to the tool housing or to let the debris barrier shift to open a bypass. In the prior designs that used cup seals looking uphole for example, if the screen in the tool plugged as the tool was removed the well could experience a vacuum or swabbing if a bypass around the cup seal were not to open.
Typical of the latter type of designs is U.S. Pat. No. 6,250,387. It accepts debris in FIG. 3 at 11 and all the debris has to clear the ball 12 that acts as a one way valve to retain debris if the circulation is stopped. Debris plugs this valve. The screen 6 is on the tool exterior and is subject to damage in handling at the surface or running it into the well. That screen filters fluid entering at 7 as the tool is removed. It has an emergency bypass 20 if the screen 6 clogs during removal operations. It relies on a large mandrel having a passage 3 which limits the volume available for capturing debris. By design, the cup 5 is always extended.
U.S. Pat. No. 7,188,675 again has a large mandrel passage 305 and takes debris laden fluid in at 301 at the bottom of FIG. 4. It uses internal pivoting valve members 203 shown closed in FIG. 5a and open in FIG. 5b. These valves can foul with debris. It has an exterior screen 303 than can be damaged during handling or running in. Its diverter 330 is fixed.
Finally U.S. Pat. No. 6,776,231 has externally exposed screen material 4 and a debris valve 20 shown in FIG. 3 that can clog with debris. It does show a retractable barrier 9 that requires a support for a part of the tool 7 in the wellbore and setting down weight. However, this barrier when in contact with casing has passages to try to pass debris laden flow and these passages can clog.
Well cleanup tools with barriers that function when movement is in one direction and separate when the tool is moved in the opposite direction are shown in Palmer US Application 2008/0029263. Other articulated barriers are illustrated in U.S. Pat. No. 6,607,031 using set down weight and U.S. Pat. No. 7,322,408 using an inflatable and a pressure actuated shifting sleeve that uncovers a compressed ring to let it expand and become a diverter.
The present invention features one or more of an internal screen, an outer housing for structural support to allow a smaller mandrel and more volume for debris collection, top entry of the debris into the collection volume to eliminate valves that can clog with debris and articulated diverters or diverter to direct debris laden fluid into the tool at the bottom and/or at the top to keep debris from falling into an annular space around the exterior of the tool that may have gotten through the screen or was for some other reason in the wellbore. These and other features of the present invention will be more apparent to those skilled in the art from a review of the description of the various embodiments and the associated drawings with the understanding that the full scope of the invention is given by the claims.